1. Field of the Invention
The present invention relates to an electrophotographic photosensitive material displaying improved sensitivity characteristics and improved durable potential stability. In particular, the present invention relates to an electrophotographic photosensitive material having a photosensitive layer containing an azo pigment having a specific coupler component.
2. Related Background Art
Hitherto, there were known electrophotographic photosensitive materials using, as the photosensitive component, inorganic photoconductive materials, such as selenium, cadmium sulfide, and zinc sulfide.
On the other hand, a variety of organic photoconductive materials have been developed because specific organic compounds can display the desired photoconductivity. For example, there are known organic photoconductive polymers, such as poly-N-vinyl carbazole and polyvinyl anthracene; low molecular weight organic photoconductive material, such as carbazole, anthracene, pyrazolines, oxadiazoles, hydrazones and polyaryl alkanes; and organic pigments and dyes, such as phthalocyanine pigment, azo pigment, cyanine dyes, polycyclic quinone pigment, perylene pigment, indigo dyes, thioindigo dyes and squalinecic acid methine dyes. In particular, a variety of photoconductive organic pigments and dyes have been disclosed since these organic pigments and dyes displaying the desired photoconductivity can be easily prepared compared to in organic materials and the variation for selecting compounds displaying photoconductivity in a desired wave length region has been widened.
For example, electrophotographic photosensitive material using an azo pigment displaying photoconductivity as a charge generating material in a functionally divided photosensitive layer having a charge generating layer and a charge transporting layer, is known. Such materials were disclosed in U.S. Pat. Nos. 4,123,270, 4,247,614, 4,251,613, 4,251,614, 4,256,821, 4,260,672, 4,268,596, 4,278,747, and 4,293,628.
Since the electrophotographic photosensitive materials using such organic photoconductive material can be prepared by painting them with a suitably selected binder, they can display a significantly improved productivity. As a result, a cost reduced photosensitive material can be provided. In addition, an advantage can be also obtained that the photosensitive wavelength region can be controlled as needed by selecting the organic pigments properly. However, such photosensitive materials can display poor sensitivity and durability with respect to those involved by inorganic photosensitive materials.
There is a disazo pigment disclosed in Japanese Patent Laid-Open No. 60-209740. This disazo pigment serving as the moiety adjacent to the coupler portion of the azo pigment used in the present invention.
However, this disazo pigment suffers from poor residual potential and stability after being used repeatedly.